This application is based on and claims priority under 35 U.S.C. xc2xa7119 with respect to a Japanese Patent Application 2001-085486 filed on Mar. 23, 2001, the entire content of which is incorporated herein by reference.
This invention generally relates to a hydraulic control apparatus. More particularly, the present invention pertains to an automatic transmission provided with a hydraulic control apparatus for controlling operation of a controlled object in response to a control pressure outputted from a plurality of control valves.
A known hydraulic control apparatus for an automatic transmission including a plurality of controlled objects is provided with a linear solenoid valve and a control valve for each controlled object for controlling respective operations of the controlled objects. The linear solenoid valve generates modulated pressure corresponding to electric current applied to the linear solenoid valve and outputs the modulated pressure to the corresponding control valve. The control valve generates control pressure corresponding to the modulated pressure discharged from the linear solenoid valve and outputs the control pressure to the corresponding controlled object. The operation of each controlled object is controlled in response to the control pressure supplied from the corresponding control valve.
Known hydraulic control apparatus with the above described structure are generally provided with an individual linear solenoid valve for each control valve. However, linear solenoid valves may be more costly as compared to other valves including a shift valve. Further, the circuit structure for electrically exciting the linear solenoid valve may be complicated. These drawbacks may thus lead to an increase in the overall manufacturing cost.
To overcome the above-described drawbacks, somewhat recent developments have led to a hydraulic control apparatus in which plural control valves with no need to output the control pressure substantially at the same time can share the same linear solenoid valve. For example, a hydraulic control apparatus illustrated in FIG. 9 is provided with a linear solenoid valve 91, a first control valve 92, a second control valve 93, a shift valve 94, and an ON-OFF solenoid valve 95. The first and second control valves 92, 93 are respectively arranged in series relative to the linear solenoid valve 91 and are supplied with modulated pressure mod discharged from the linear solenoid valve 91. The first control valve 92 outputs a first control pressure in response to the modulated pressure mod introduced to the first control valve 92 from the linear solenoid valve 91 and the second control valve 93 outputs a second control pressure in response to the modulated pressure mod introduced to the second control valve 93 from the linear solenoid valve 91. The first and second control pressures are supplied to any one of controlled objects selected via the shift valve 94.
The shift valve 94 is maintained under a first operating condition in which a valve element of the shift valve 94 is biased downward in FIG. 9 when hydraulic pressure is supplied to the shift valve 94 from the ON-OFF solenoid valve 95 corresponding to electric current applied thereto. In this case, the control pressure (a first control pressure) discharged from the first control valve 92 can be outputted to the corresponding controlled object via the shift valve 94. On the other hand, the shift valve 94 is maintained under a second operating condition in which the valve element of the shift valve 94 is returned to the upper position in FIG. 9 when hydraulic pressure is not supplied to the shift valve 94 from the ON-OFF solenoid valve 95. In this case, the control pressure (a second control pressure) from the second control valve 93 can be outputted to the corresponding controlled object via the shift valve 94.
As described above, the modulated pressure mod is introduced to the first and second control valves 92, 93 from the linear solenoid valve 91, and the control pressure outputted from each of the control valves 92, 93 corresponding to the modulated pressure mod is selectively outputted to any one of the controlled objects via the shift valve 94.
However, the hydraulic control apparatus for the automatic transmission having the above construction may suffer from the following drawbacks. The modulated pressure mod needs to be outputted to the first and second control valves 92, 93 only from the linear solenoid valve 91 substantially at one time. Therefore, the linear solenoid valve 91 may be overloaded which may lead to a deterioration in response of the controlled objects.
Accordingly, the above disclosed hydraulic control apparatus for the automatic transmission is susceptible of certain improvements with respect to improving the response of the controlled objects to be controlled in response to the control pressure outputted from the plural control valves.
A hydraulic control apparatus includes a linear solenoid valve for outputting modulated pressure in response to electric current applied to the linear solenoid valve, a plurality of control valves outputting control pressure in response to the modulated pressure introduced from the linear solenoid valve, a shift valve for switching between the control valves to which is to be introduced the modulated pressure in response to hydraulic pressure supplied to the shift valve, and an ON-OFF solenoid valve for switching the supply of the hydraulic pressure to the shift valve in response to electric current applied to the ON-OFF solenoid valve.
The hydraulic control apparatus can improve the response of the controlled objects to be operated in response to the control pressure outputted from the plural control valves.
The linear solenoid valve is preferably arranged at a downstream side of the shift valve. Thus, if air is placed into the shift valve, the air can be discharged from the linear solenoid valve. Accordingly, the hydraulic control apparatus can effectively inhibit or prevent slow response of the controlled objects and/or generation of vibration while also facilitating or ensuring a stable performance.
According to another aspect of the present invention, an automatic transmission with the hydraulic control apparatus is provided with plural friction engaging elements for changing a shift stage through combinations of engaged and disengaged conditions of the friction engaging elements based on the control pressure supplied to the friction engaging elements. The shift valve further switches the supply of the control pressure supplied to the plural friction engaging elements. Therefore, other components are not additionally required for the automatic transmission with the hydraulic control apparatus.
The plural control valves include a pair of control valves outputting the control pressure to each friction engaging element associated with any one of the shift stages at a higher speed and to each friction engaging elements associated with any one of the shift stages at a lower speed. The shift valve for switching the supply of the control pressure supplied to the plural friction engaging elements is switched over upon shifting of the shift stage between the higher speed stage and the lower speed stage. Therefore, the plural control valves and the shift valve are effectively operated in relation to one another to perform an appropriate shifting control.
According to another aspect, an automatic transmission control system includes a linear solenoid valve for outputting modulated pressure in response to electric current applied to the linear solenoid valve, a start control valve and a lock-up control valve which output control pressure in response to the modulated pressure introduced from the linear solenoid valve, plural friction engaging elements to be engaged and disengaged in different combinations based on the control pressure to change a shift stage, a shift valve operable in response to hydraulic pressure supplied to the shift valve for switching between introducing the modulated pressure to the start control valve and introducing the modulated pressure to the lock-up control valve to switch the friction engaging elements to which the control pressure is supplied, and an ON-OFF solenoid valve switching supply of the hydraulic pressure to the shift valve in response to electric current applied to the ON-OFF solenoid valve.